This invention relates generally to shaft assemblies and, more particularly, to a mechanism and method for delashing a shaft assembly.
One problem associated with shaft assemblies involves axial play or backlash between the shaft and the components to which it is mounted. This backlash, which is a function of the manufacturing and assembly tolerances associated with the shaft assembly components, may cause uneven wear, noise, and poor response when the axial position of the shaft shifts from a predetermined desired position. Examples of shaft assemblies which may experience these problems include worm gear assemblies, ball-screw/ball-nut drives, and power telescoping steering systems. In power telescoping steering systems, for example, a small gear set mounted to a shaft is used to actuate the steering column telescoping function. In each of the above cases, due to stack-up component tolerances and the loads applied to the shaft, there is a potential for axial clearance and lash in the shaft, resulting in the previously noted problems.
Methods for alleviating axial backlash in the shaft assembly include the application of either a tensile or compressive axial load to the shaft, to adjust the axial position of the shaft and to maintain the shaft in a predetermined (and, ideally, lash-free) position. One existing method of applying the axial loads is via a set screw mounted in a threaded hole formed coaxially with the shaft. The screw is turned until contact is made with a polymeric cap applied to an end of the shaft to be delashed. Additional turns of the screw drive the screw more deeply into the hole and cause the screw to bear down on the end of the shaft, thereby applying an axial compressive load which delashes the shaft. However, this delashing method is labor-intensive and relatively time-consuming, because the screw must be adjusted back and forth within the hole while the motor electrical current is monitored to ascertain the amount of compression on the shaft and the resulting suitability of the delash setting. In addition, it is desirable to either prevent or remove the axial backlash without adding substantial friction to the assembly which would degrade the overall performance.